Current Monolithic Microwave Integrated Circuits (MMICs) technologies, developed using semiconductors like, InP, GaAs, SiGe, GaN, etc., are typically not suitable for operating at higher-millimeter-wave and submillimeter-wave frequencies. FIG. 1 depicts a lower half of a conventional MMIC module split-block 1. The close-up view 2 of the MMIC module 1 shows the MMIC-to-waveguide transitions 3 being bonded to a conventional MMIC chip 4 with wire bonding 6. The MMIC chip 4 was designed on a 50 μm thick InP substrate in the channel of a split-waveguide block.
FIG. 2 depicts a cross-section of another conventional MMIC chip 10. The conventional MMIC chip 10 may contain devices 12, on a substrate 11, that are connected to a Grounded Coplanar Waveguide (GCPW) (not shown) or to microstrip transmission mediums 14 that may be connected to a ground plane 16 through ground pads 15 and substrate vias 17. As known in the art, the devices 12 may be formed through a frontside processing of a wafer containing the MMIC chip 10.
At high-mm-wave and sub-mm-wave frequencies, the transmission mediums 14 exhibit high-parasitic effects with high loss values when disposed on the thick semiconductor substrate 11. Further, when the conventional MMIC chip 10 is placed in a waveguide module 20, the performance of the MMIC degrades due to parasitic effects. FIG. 3 depicts a conventions MMIC chip disposed on a waveguide module 20. The waveguide module 20 may contain an upper split-block section 26 disposed above the MMIC chip 10; a lower split-block section 25 disposed below the MMIC chip 10; an input waveguide 27 formed by the upper split-block section 26 and the lower split-block section 25; an output waveguide 28 formed by the upper split-block section 26 and the lower split-block section 25; low-loss substrates 22 containing transitions 24 that are wirebonded 21 to the MMIC chip 10; metal patterns 23 disposed under the MMIC chip 10 and substrates 22 for transitions 24; and an epoxy (not shown) that may be used to hold the MMIC chip 10 and the substrates 22 on the lower split-block section 25.
The high-losses introduced by transmission mediums 14 and substrate-moding effects introduced by semiconductor substrate 11 tend to degrade conventional MMIC chip 10's performance at submillimeter wave frequencies.
According to the present disclosure, MMIC chips formed using suspended membrane transmission structures exhibit lower loss at higher-millimeter-wave and submillimeter-wave frequencies and help to minimize parasitic modes in a waveguide environment. Further, according to the present disclosure, MMIC chips formed using suspended-substrate structures also present better performance than conventional MMIC chips at higher mm-wave and submm-wave frequencies.